Apparatus for making permanent magnet rotor

ABSTRACT

A permanent magnet rotor for an electronically commutated motor (ECM) has a core, a plurality of magnetizable elements spaced around the core, and a thin-walled retaining shell which has been stretched around the core and magnetizable elements to hold the elements in position. The rotor is made by an inventive method which involves axially aligning the core and surrounding magnetizable elements with the retaining shell, and cold-pressing the retaining shell over the core and elements to sandwich the elements between the shell and core. The core and magnetizable elements serve as a mandrel about which the shell is reformed in a cold working operation. Other aspects of the invention include the fixturing apparatus used to align the core and magnetizable elements with the retaining shell, and apparatus which is used to evenly space the magnetizable elements around the core and hold the elements in position during at least a portion of the cold-pressing operation. Additional features of certain embodiments of the rotor of the present invention include end plates axially disposed adjacent the ends of the rotor core and magnetizable elements, and the use of adhesives between the core and magnetizable elements and/or the ends of the core and magnetizable elements and the end plates.

FIELD OF INVENTION

This is a divisional application from Ser. No. 07/872,551, filed Apr.23, 1992, 5,563,463 which is a division from Ser. No. 07/721,689, filedJun. 26, 1991, now U.S. Pat. No. 5,144,735, which is a division fromSer. No. 07/459,633, filed Jan. 2, 1990, now U.S. Pat. No. 5,040,286,which is a continuation-in-part from application Serial No. 07/203,942,filed Jun. 8, 1988, abandoned. The present invention relates generallyto permanent magnet rotors for electric motors, and more specifically toa novel rotor having particular application in electronically commutatedmotors (ECMS) operable at relatively high rotor speeds, and to a novelmethod and apparatus for making the rotor.

BACKGROUND OF THE INVENTION

Permanent magnet rotors for ECM motors typically comprise a solid orlaminated iron core, surrounded by a plurality of magnetic elements. Thematerials typically used to form the magnetic elements include barium orstrontium ferrite (traditional ferrite magnets) and samarium cobalt(rare-earth magnets). The former are often referred to as ceramicmagnets and are generally manufactured by pressing a granular orpowdered ferrite material into a mold of desired shape, and "firing" orheating the molded element in a kiln until cured. Permanent magnetrotors of this type are used primarily in electric motors and inconjunction with control circuitry and other associated apparatus of thetype as disclosed, for example, in the following United States patents(as well as the assigned to the assignee of the present application andincorporated herein by reference: U.S. Pat. No. 4,456,845 (Cunningham);U.S. Pat. No. 4,466,165 (Otto); U.S. Pat. No. 4,476,736 (Hershberger)and related divisional applications listed therein; U.S. Pat. No.4,654,566 (Erdman) and related continuation and continuation-in-partapplications listed therein; and U.S. Pat. No. 4,686,436 (Archer).Rotors produced in accordance with the present invention can be used toparticular advantage in hermetically sealed refrigeration compressorapplications where exposure to refrigeration and/or lubricating fluidsis likely to occur, and where relatively high efficiency ratings may berequired.

Due to the relatively high mass of the materials used to form thepermanent magnetic elements disclosed in the aforelisted patents, andthe relatively high (1,000-16,000 RPM) rotor speeds developed in theassociated motors, retention of the magnetic elements in positionadjacent the rotor core is a serious concern. A number of methods andtechniques for retaining magnetic elements on the rotor core havepreviously been used or considered. One such technique involvespositioning the magnetic elements around the outer diameter of the core,and applying a wrap of Kevlar or fiberglass to hold the magnets inplace. The Kevlar or fiberglass used is typically a fine strandedmaterial which is pulled through epoxy prior to wrapping. An adhesivefiller may be applied to the wrapped rotor to fill voids and provide amore rigid construction. A drawback in this technique, however, is thatthe ends of the stranded material are difficult to attach to the rotorcore, and the nature of the materials involved may create problems inthe working environment. Additionally, use of this technique isrelatively expensive and time consuming, and uniformity and tolerancesof the finished product can be difficult to control.

Another technique for retaining the magnets on the core involveswrapping a relatively fine wire, under tension, around the magneticelements, followed by application of an adhesive or epoxy overcoat tothe assembly to protect the metal wire. As with the fiberglass wraptechnique discussed above, proper attachment of the wire ends to thecore is difficult and relatively expensive to achieve. This technique isalso time consuming and labor intensive, and involves a number ofdistinct operations which may be difficult and costly to automate forthe production-setting.

Another technique for retaining magnets around a rotor core involves theuse of a cylindrically shaped shell or "can" which is disposed aroundthe outer peripheral surface of the magnet/core sub-assembly to hold themagnets in position. The outer shell is typically formed of anonmagnetic steel such as INCO-718 (Inconel) or beryllium-copper. Atleast three techniques for assembling a permanent magnet rotor whichuses such a retaining shell have been previously developed. One of thesetechniques is understood to have originated with Hitachi, Ltd. of Japanand is believed to involve placing a core and magnetic elements in ashell, die casting molten aluminum into the shell to lock the magneticelements and core in place, and forming end rings at the ends of therotor so as to completely cover the magnetic elements. The shells ofthese rotors appear to be formed from a 300 series stainless-steelhaving a relatively thick-walled construction which is machined afterdie-casting to a final wall thickness varying between 0.015" and 0.025",depending on point of measurement.

Another technique for assembling an outer retaining shell onto acore/magnet sub-assembly is described in U.S Pat. No. 4,549,341 toKasabian. This patent discloses a rotor formed from a shaft (10) turnedto provide a central area (20) having a larger outer diameter thanaxially adjacent end areas (15 and 24). A plurality of flat faces (30)are formed on the larger diameter portion and each flat has a steelblock (50) mounted thereon conforming in shape to a permanent magnet tobe ultimately carried on the shaft. A layer of non-magnetic material(60) (e.g., aluminum) is cast around the larger diameter portion of theshaft and attached blocks, and machined to a diameter slightly largerthan the desired finished diameter. The blocks are then removed andreplaced with permanent magnets (80) which are typically rare-earthpermanent magnets formed of samarium cobalt or Al-nickel 6 and areretained in the apertures by magnetic attraction to the shaft or,alternatively, by an adhesive material. After the magnets are installed,the magnets and adjacent casting surfaces are machined to the desiredfinished diameter, and an outer non-magnetic steel shell, such asINCO-718, is installed over the magnets by heat shrinking to provide aninterference fit between the shell and the underlying casting andpermanent magnets. Other patents which disclose the use of a heat-shrinktechnique for installing a retaining shell over a rotor core andsurrounding magnets include U.S. Pat. Nos. 3,531,670 and 3,909,677 whichare assigned to The Bendix Corporation, and U.S. Pat. Nos. 4,242,610,4,332,079, 4,339,874, and 4,445,062 and a number of related patentsassigned to the Garrett Corporation.

U.S. Pat. No. 4,617,726 (Denk) discloses an alternative technique forinstalling an outer shell (110) over a rotor sub-assembly (50). Thistechnique utilizes a tubular housing (120) in which the outer shell(110) is supported and subjected to hydraulic pressure so as to causethe tubular shell to expand radially outwardly. The rotor sub-assembly(50) is forced axially into the expanded shell by a ram to effect auniform fit between the rotor sub-assembly and the surrounding shell.

Each of the aforedescribed techniques for installing a retaining shellover a core and surrounding magnetic elements has limitations anddisadvantages. One disadvantage is the requirement for separate castingand machining operations which are costly, time consuming, andpotentially injurious to the magnetic elements. The die castingtechnique initially requires a shell having a relatively large wallthickness due, at least in part, to conditions attendant to die-castingoperations. A machining operation is generally required to reduce thewall thickness of the shell in order to avoid relatively large losses inefficiency.

The described heat-shrink technique is also potentially injurious to themagnetic elements since the heat to which the magnetic elements areexposed can cause the magnetic materials to crack and chip.Additionally, the amount of expansion which can be achieved by heatingthe shell is limited. For example, the diameter of a shell for athree-inch diameter rotor will increase approximately 0.017" whenheated. Accordingly, the machining step required by Kasabian prior toheat-shrink installation of his retaining sleeve must be precise toensure a high interference fit after cooling of the sleeve. Machiningoperations of the type described by Kasabian are generally not practicalwhen ferrite or other ceramic magnetic elements are used because suchmaterials are very expensive to machine and cut. Moreover, the materialsand techniques conventionally used in the manufacture of ceramic magnetslead to relatively wide variations in dimensional tolerances. Forexample, ferrite magnetic elements of the size which might typically beused with a three-inch diameter rotor may vary by 0.020" in thickness.The overall diameter of the core and surrounding magnetic elements mayvary by up to 0.040". Thus, ferrite magnetic element cannot routinely beused in heat-shrink assembly techniques due to the inherent dimensionallimitations. Although the hydraulic expansion technique disclosed inU.S. Pat. No. 4,617,726 avoids possible damage to the magnets inherentin the heat-shrink method, this technique does not address the problemsassociated with dimensional variations in the magnetic elements andcore.

SUMMARY OF THE INVENTION

One of the primary objects of the present invention is to provide anovel permanent magnet rotor assembly which is particularly tolerant ofsubstantial dimensional tolerance variations in the magnetizableelements.

Another object of the present invention is to provide a novel method andapparatus for making a permanent magnet rotor which provide relativelylow cost ease of manufacture and result in optimum magnetic elementretention.

A more particular object of the present invention is to provide a novelpermanent magnet rotor assembly employing a core having magnetizableelements surrounding the core, a sleeve securing the magnetizableelements radially against the core so as to prevent longitudinalmovement of the magnetizable elements relative to the core, and endrings retained against the opposite ends of the core so as to retainparticles within the rotor assembly in the event of chipping or crackingof the magnetizable elements, a void being formed between at least oneof the end rings and the adjacent magnet ends.

Another object of the present invention is to provide a novel permanentmagnet rotor and method and apparatus for making the rotor which arehighly tolerant of substantial dimensional variations so as to assure ahigh-interference fit between a plurality of magnetizable elements and aretaining shell irrespective of dimensional variations.

Still another object of the present invention is to provide a rotorstructure which is extremely durable, easy to manufacture and relativelyinexpensive.

A further object of the present invention is to provide a novel rotorassembly fixture for holding a rotor core and surrounding magnetizableelements in precise relation relative to a cylindrical retaining shell,and which effects uniform pressure application to an end edge of theshell to plastically and elastically deform the shell as it iscold-pressed axially over the core and magnetizable elements.

The aforementioned objects of the present invention may be achieved inaccordance with one method of making a permanent magnet rotor whichincludes the steps of placing a plurality of magnetizable elementsaround a core and temporarily holding the elements in position, axiallyaligning the core and surrounding magnetizable elements with a retainingshell, and cold-pressing the retaining shell over the core andsurrounding magnetizable elements to permanently retain the magnetizableelements in position around the core.

As used herein, the term "magnetizable elements" refers to elementswhich are, or which may be, magnetized, and is intended to includeelements such as magnetic elements and functional equivalents thereof,whether or not such elements are in a magnetized condition. It iscontemplated that under certain conditions it may be desirable toassemble rotors according to the present invention using magnetizableelements which are in amagnetized condition prior to or at the time ofassembly. On the other hand, it may also be advantageous to assemble arotor using magnetizable elements which have not been magnetized, butwhich are subsequently magnetized prior to actual usage of the rotor.

In one embodiment of the invention, the permanent magnet rotor includesa layer of adhesive which is applied to the outer periphery of the coreprior to placing the magnetizable elements around the core. A pair ofannular end plates are positioned in axially aligned abutting relationto opposite ends of the core which is made to a relatively preciselongitudinal length longer than the magnetizable elements so that atleast one of the end plates is spaced from the corresponding ends of themagnetizable elements. A layer or bead of epoxy adhesive is selectivelyapplied to the ends of the magnets which are spaced from thecorresponding end plate so as to create a partial void between the endsof the magnetizable elements and the spaced end plate when the epoxy iscured.

In yet another embodiment of the invention, the step of placing themagnetizable elements around the core includes the additional step ofpositioning the magnetizable elements so as to assure substantiallyequal circumferential spacing between adjacent elements, and the step oftemporarily holding the magnetizable elements in position around thecore includes clamping each element in position against the core. Thestep of cold-pressing the retaining shell axially over the core andsurrounding magnetizable elements includes applying a substantiallyuniformly distributed force to a continuous end surface of the retainingshell to plastically and elastically deform the shell to fit over themagnetizable elements.

The method of the present invention is preferably performed in a presshaving a rotor assembly fixture defining a working axis (i.e., an axisalong which the force generated by the press acts) and on which therotor core is mounted such that a central axis of the core is coaxiallyaligned with the working axis of the press. The core is mounted on abolt support having a base end received within a base fixture portion ofthe press. A shank extends upwardly from the base of the bolt supportand is received through a central bore of a rotor core when mounted onthe bolt support. An alignment guide is mounted on the upper end of theshank and serves to receive and align an annular guide sleeve which, inturn, aligns the rotor shell with the core and magnetizable elementswhen assembled about the core.

The rotor assembly further includes a cylindrical assembly sleeve whichis attached to a working cylinder of the press and has an axial bore ofa diameter substantially equal to the inner diameter of the rotor shell.The assembly sleeve has a sharp annular edge surface peripherally of itsaxial bore for contacting the continuous edge surface of a rotor shellso as to apply a substantially uniform force to the upper edge surfaceof the shell during assembly of the rotor shell axially over the coreand surrounding magnetizable elements.

A feature of the rotor assembly fixture of the present invention lies inthe provision of apparatus for positioning the magnetic elements incircumferential spaced relation about the core during assembly of therotor. The magnet positioning apparatus includes a plurality of gaugemembers which are supported circumferentially of the bolt support formovement radially of a core when mounted on the bolt support. Each gaugehas a wedge-shaped tip and is cooperative with an annular control ringoperative to simultaneously cam each gauge tip generally radiallybetween a corresponding pair of adjacent magnetic elements so as toeffect gauged circumferential spacing between the magnetic elements.

Another feature of the rotor assembly fixture in accordance with thepresent invention lies in the provision of clamping apparatus forreleasably clamping the magnetic elements against the peripheral surfaceof the core during assembly of the sleeve over the magnets and core. Theclamping apparatus includes a plurality of clamps which are supported ingenerally coplanar alternating relation with the gauge members. Theclamps are adapted for radial movement to engage respective ones of themagnetic elements, and include means for releasably locking the clampends in clamping position.

In accordance with yet another feature of the rotor assembly apparatusof the present invention, a plurality of dies are provided forincrementally and plastically deforming or crimping the opposite endedges of the rotor shell generally radially inwardly toward the centralaxis of the shell after the shell has been positioned over the core andsurrounding magnetic elements, and after an annular end plate has beenpositioned against each end of the core in coaxial alignment therewith.In one embodiment of the crimping apparatus, a first die deforms acircumferential edge of the shell over the peripheral edge of thecorresponding end plate through an angle of approximately 30°, a seconddie further deforms the edge through an angle of approximately 60°, anda third die further deforms the edge to an angle of approximately 90°.so that an integral end flange is formed on the shell which lies in aplane normal to the longitudinal axis of the sleeve. The third die ispreferably provided with an elastically deformable insert whichsurrounds and grips the corresponding end of the metallic shell duringthe crimping operation.

Use of the method and assembly apparatus of the present inventionfacilitates construction of a rotor which is highly tolerant of arelatively wide range of dimensional variations in the magnetizableelements which surround the core while assuring fixed longitudinalretention of the magnetizable elements relative to the core. In priorheat shrink and hydraulic expansion techniques of the aforementionedtype, the dimensional variations in core diameter and magnetic elementthickness must be controlled in a very exacting manner in order toobtain a desired fit between the various components of the rotor. Inaccordance with the present invention, the outer retaining shell iscold-formed around the core and surrounding magnetizable elements whichact as a mandrel to radially deform the shell. This enables the use ofrelatively inexpensive ceramic magnetizable elements which, in amagnetic element having a radial thickness of approximately 0.4"-0.5",may have a dimensional tolerance range of about 0.020" or more (i.e., 5%or greater). Such dimensional variations in the overall diameter of thecore and surrounding magnetizable elements cannot be tolerated by knownheat-shrink and hydraulic expansion rotor assembly techniques.

Other objects, advantages and features of the present invention willbecome apparent from the following detailed description of the inventionwhen taken in conjunction with the accompanying drawings wherein likereference numerals designate like elements throughout the several views.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a permanent magnet rotor constructed inaccordance with the present invention;

FIG. 2 is an exploded view of the rotor of FIG. 1;

FIG. 3 is an elevational view of the rotor of FIG. 1, but with portionsbroken away for clarity;

FIG. 4 is an exploded view of a portion of the apparatus used toassemble the rotor of FIG. 1;

FIG. 5 is a fragmentary longitudinal sectional view of the apparatus ofFIG. 4 in assembled relation and further illustrating fragmentaryportions of gauging and clamping members for the magnetizable elements;

FIGS. 6(a), 6(b) and (c) are longitudinal sectional views of theapparatus of FIG. 4 illustrating cold-forming of a shell over a core andsurrounding magnetizable elements in accordance with the presentinvention;

FIG. 7 is an enlarged fragmentary detail view of the portion of FIG.6(b) encircled at "A";

FIGS. 8 (a)-8(f) illustrate the sequence of crimping an end of a magnetretaining shell after assembly onto a core;

FIGS. 9(a) and 9(b) are fragmentary plans and side elevational views,respectively, of apparatus for circumferentially spacing and clampingmagnetizable elements arou he core during assembly;

FIG. 10 is a plan view similar to FIG. 9(a) but with the magnet spacinggauge n operative positions; and

FIGS. 11(a) and 11(b) are plan and side elevational views, respectively,similar to FIGS. 9(a) and 9(b) but with both the spacing and clampingdevices in operative positions.

DETAILED DESCRIPTION

Referring now to the drawings, and in particular to FIGS. 1-3, apermanent magnet rotor constructed in accordance with the method andapparatus of the present invention is indicated generally at 10.Briefly, rotor 10 includes a rotor core 12, a pair of annular end plates14a and 14b, a plurality of arcuate shaped magnetizable elements 15, andan outer magnet retaining shell 16 which retains the magnetizableelements securely against the core to prevent longitudinal movement ofthe magnets relative to the core. As will be described, during assemblyof the rotor, end portions of the shell which extend longitudinallybeyond the ends of the core 12 are formed or crimped radially inwardlyto retain the end plates 14a,b against the ends of the core in coaxialrelation therewith. A void or gap is formed between at least one of theend plates 14a,b and the adjacent end surfaces of the magnetizableelements 15.

The core 12 is illustrated as comprising a solid metallic or sinterediron cylindrical core having a longitudinal cylindrical bore 18extending axially through the core and defining a central axis 20.Alternatively, the core 12 nay be made as a laminated metallic corewhich may be preferred in some applications.

In the illustrated embodiment, three magnetic or magnetizable elements15 are employed which comprise similarly shaped arcuate ceramicmagnetizable elements. As aforementioned, the term "magnetic elements"also includes magnetizable elements since, at the time of assembly witha core 12 to form the rotor 10, the magnetizable elements may or may notbe in a magnetized condition. Each magnetic element 15 has an innerarcuate surface 24 having a radius of curvature substantially identicalto the radius of the outer cylindrical surface 26 of the core so as tofit against the core when the rotor 10 is assembled. Each magneticelement has an arcuate extent enabling the magnetic elements to beplaced against the outer core surface 26 between equally angularlyspaced longitudinal ribs or beads 26a formed on the outer core surface,as illustrated in FIG. 2. The ribs 26a assist in preventing rotationalsliding of the magnetic elements relative to the core during operation.

At least one end, and preferably both ends, of each magnetic element 15is provided with an outer radial edge or chamfer 28 to aid in theassembly process. Conventionally, the ceramic magnetic elements aremanufactured by techniques which result in relatively wide dimensionalvariations in both longitudinal length and radial thickness. Forexample, a typical magnetic element employed in a rotor according to thepresent invention may have a nominal wall thickness of 0.420", atolerance range on the inside radius of ±0.005", and a tolerance rangeon the outside radius of ±0.005", resulting in an overall radialthickness tolerance range of 0.020".

In the illustrated embodiment, the end plates 14a and 14b compriseidentical flat aluminum rings or annular washers having an outer radius32 preferably equal to or slightly less than the combined minimum radiusof the cylindrical surface 26 of core 12 and the arcuate magneticelements 15 when assembled onto the core. Each end plate has an innerradius 34 larger than the radius of bore 18 in core 12, and preferablysmaller than the radius of the outer cylindrical surface of the core.The primary function of the end plates 14a and 14b is to prevent brokenpieces or fragments of the magnets from leaving the rotor assembly andcontaminating the interior of a motor or getting into the air gap. Inthis respect, the end rings 14a and 14b also assist in maintaining acracked magnetic element in operational position longitudinally relativeto core 12.

The rotor shell 16 is preferably made from a non-magnetic metal, such as304 stainless steel tubing. The wall thickness of shell 16 is preferablyless than 0.020", with satisfactory results having been obtained withwall thicknesses of between approximately 0.008" and 0.012". A shellwall thickness of about 0.004"-0.006" may also be satisfactory. Ingeneral, a decrease in the shell wall thickness will result in adecrease in losses due to eddy currents flowing in the shell and theability to decrease the size of the air gap between the rotor andstator. The particular material used for forming the shell and theretention strength desired are other factors affecting the shell wallthickness selected.

The initial inner diameter 36 of shell 16 is slightly less than theminimum combined diameter of core 12 and the magnetic elements 15 whenassembled against the core.

Shell 16 has a longitudinal length greater than the longitudinal lengthof the core 12 plus the thickness of the end plates 14a and 14b, anddefines opposite continuous circular end edge surfaces 38a and 38b whichlie in planes perpendicular to the longitudinal axis of the shell. Aswill be described, the opposite ends of the shell are subsequentlycrimped or formed radially inwardly toward the central axis 20 of core12 so as to overlap and bear against the end plates and retain themfirmly against the ends of the core.

The magnetic elements 15 have longitudinal lengths less than the lengthof core 12. In this manner, when the magnetic elements are supported ina vertical orientation surrounding the core 12 with their lower endsengaging the lower end plate 14b during assembly of the rotor, a gap isformed between the upper ends of the magnets and the upper end plate14a. The gap 40 is intentional and may vary in width by the range of thecombined tolerances of the lengths of core 12 and magnetic elements 15.The core length is preferably held to a relatively close tolerance rangeso that the variation in width of the gap 40 is primarily the result ofvariations in the longitudinal lengths of the magnetic elements 15. Forexample, if a solid core construction is used, a close tolerance rangefor the core length may be readily obtained. However, conventionalmanufacturing techniques employed in making ceramic magnetic elementsresult in the longitudinal lengths of the magnetic elements varying byup to 1/8" for magnetic elements which are 4.0"-6.0" in length. Thus,the extremes of tolerance build-up between the core and magneticelements will result in a gap 40 which may vary by up to 1/8" or more.

As will later be described, during assembly a generally circular bead ofadhesive 42, such as EPON 828 epoxy, is applied to the upper ends of themagnetic elements 15 in an amount sufficient to fill approximately40%-80% of the gap 40 when the upper end plate 14a is assembled againstthe upper end of the core 12. Thus, after curing, at least 20% of thevolume of the gap 40 remains void. Other adhesives may be used providedthey are suitable for the environment in which the rotor will beemployed. An adhesive, such as EPON 828 epoxy, is also preferablyprovided between the outer peripheral surface 26 of core 12 and theinner arcuate surfaces 24 of the magnetic elements 15, and at theinterface 46 between the lower end plate 14b and the adjacent lower endsof the core 12 and magnetic elements 15 so as to cover a minimum of 80%of the interfacing surface areas, respectively, between the outerperiphery of the core and surrounding magnetic elements, and between thelower end plate 14b and the adjacent lower ends of the magnets and core.

In accordance with one feature of the present invention, apparatus isprovided to assemble the rotor 10 of FIGS. 1-3. Referring to FIGS. 4 and5, the assembly apparatus includes an upper shell mounting fixture 48adapted for attachment to a vertically movable ram 49 of a conventionalpress or like device (not shown) for exerting a downward force F on thecomponents of rotor 10. The shell mounting fixture 48 is in the form ofa generally cylindrical sleeve having a closed upper end and an innercylindrical bore 50 of a diameter substantially equal to the initialinner diameter 36 of shell 16. A lower annual edge 52 of end surface 54immediately adjacent bore 50 is adapted to uniformly contact the upperend edge 38a of shell 16 so that a downward force F may be uniformlyapplied to shell 16.

The assembly apparatus includes a lower support fixture, a fragmentaryportion of which is indicated at 56, adapted to be mounted on a lowerbed or platform (not shown) of the press in coaxial relation withfixture 48. A bolt assembly 58 is supported on the support fixture 56and serves to support the core 12, magnetic elements 15 and end plates14a and 14b during the assembly process. The bolt assembly 58 includes abase end 60 having parallel wrench flat surfaces 62 formed on acylindrical portion 64 which is adapted to be snugly received within acavity 66 in the support fixture 56. An alignment pin 68 extendsupwardly from the bottom of cavity 66 and is received within a blindbore 70 in the base end 60 of bolt assembly 58 so as to establish apredetermined orientation between the support fixture 56 and boltassembly 58. The bolt assembly 58 has an alignment pin 72 which extendsupwardly from the base end 60 and is received within a locating bore 74(FIGS. 3 and 5) formed in the end of core 12 so as to establishpredetermined angular orientation between the core and the boltassembly. A cylindrical boss 78 is formed on a transverse surface 76 onthe base end 60 of bolt assembly 58 and has a diameter sufficient toreceive and locate end plate 14b coaxially on the bolt assembly. Acylindrical boss 80 extends coaxially upwardly from the boss 78 and issnugly received within the core bore 18 during the assembly process.

A shank or connecting rod 82 is affixed coaxially to the boss 80 andextends upwardly a distance sufficient to extend through the core bore18 and through an upper alignment guide or cap 84. The alignment guide84 has a cylindrical pilot portion 86 adapted to be snugly receivedwithin the upper end of the core bore 18, and has a cylindrical locatingboss 90 adapted to snugly fit within the central opening 94 in the upperend plate 14a when positioned on the upper end of the core. A washer 96and nut 98 are mounted on an upper threaded end of the shank 82 tosecure the alignment guide against the upper end of the core.

The rotor assembly fixture includes a cylindrical shell guide 100 havingan outer diameter 102 slightly less than the initial inner diameter 36of shell 16 so that shell will slide axially over the shell guide in asnug but non-interfering manner. The shell guide has a coaxial bore 104slightly greater in diameter than the diameter of a cylindrical surface106 on the alignment guide 84 such that the shell guide may bereleasably mounted coaxially on the alignment guide with the lower endsurface of the shell guide engaging the end plate 14a. In this mannerprecise axial alignment of the shell 16 with the core 12 may be obtainedduring rotor assembly. The upper outer circular edge of the shell guideis preferably chamfered at 108 to guide the shell 16 over the shellguide and facilitate entry of the shell guide into the cylindrical bore50 in fixture 48.

With a core 12 and upper and lower end plates 14a and 14b mounted on therotor assembly fixture as thus far described, three arcuate magnetic ormagnetizable elements 15 are positioned against the outer cylindricalsurface 26 of the core, with the lower ends of the magnetic elementsengaging the lower end plate 14b. As aforementioned, a suitable adhesiveis preferably applied to the upwardly facing surface of the end plate14b and to the outer cylindrical surface of the core for contact withthe corresponding interfacing surfaces of the core and magneticelements. The magnetic elements 15 are of predetermined arcuatedimension so that adjacent longitudinal edge surfaces of the magneticelements are spaced a predetermined distance apart when the magneticelements surround and engage the core between the ribs 26a. Tofacilitate predetermined arcuate spacing of adjacent magnetic elementsand clamp the magnetic elements against the core during assembly of theshell 16, gauging means and clamping means in the form, respectively, ofa plurality of spacing and gauging devices 110 and a plurality ofclamping devices 112 are supported on the base 56 in alternatingequidistantly spaced relation about the center axis of the assemblyfixture.

The spacing devices 110 are operative to simultaneously position andgauge the circumferential spacing between the magnetic elements so thatthe magnetic elements are equidistantly spaced around core 12. Theclamping devices 112 are operative to temporarily clamp the magneticelements against the core after spacing and prior to assembly of a shell16 over the core and magnetic elements. The structure and operation ofspacing devices 110 and clamping devices 112 are discussed fully below.

FIGS. 6(a), 6(b) and 6(c) illustrate sequential steps in cold-pressing ashell 16 over the sub-assembly of axially aligned core 12, end plates14a, b and surrounding magnetic elements 15. For purposes of clarity,the spacing devices 110 and clamping devices 112 are omitted from FIGS.6(a), 6(b) and 6(c).

After positioning the core, end plates 14a and 14b, and magneticelements 15 on the bolt assembly 58 and affixing the alignment guide orcap 84 onto the shank 82, the shell guide sleeve 100 is positioned onthe alignment guide 84 and a shell 16 is slipped over the guide sleeve,as shown in FIG. 6(a). The upper shell mounting fixture 48 is thenbrought downwardly to a position wherein its lower end is received overthe upper end of the guide sleeve 100 and the edge surface 52 engagesthe upper edge 38a of shell 16. The edge surface 52 is formed to assuremaximum surface contact with the edge 38aof shell 16.

Further downward movement of the shell mounting fixture 48 causes theshell 16 to undergo cold-pressing in which the shell 16 is plasticallydeformed radially outwardly as it progresses downwardly over the core 12and surrounding magnetic elements 15 as shown in FIGS. 6(b) and 6(c).The chamfers 28 on the upper outer edges of the magnetic elements 15assist in the initial outward plastic deformation of shell 16 over themagnetic elements. As an alternative, the lower end edge 38b of shell 16may be flared slightly outwardly to facilitate initial axial movement ofthe shell over the magnetic elements 15.

FIG. 7 illustrates in greater detail the plastic deformation of shell 16as it is formed downward over the core 12 and surrounding magneticelements 15 which act as a mandrel for plastically deforming the shell.In addition to plastic deformation, some elastic deformation of theshell 16 also occurs so that shell is in a state of circumferentialtension and exerts substantial inwardly directed forces on the magneticelements 15. The extent of deformation of shell 16 may be such thatmarginal edges and surface markings on the outer surfaces of themagnetic elements 15 can be observed on the outer surface of shell 16after final assembly of the rotor.

During assembly of the shell 16 onto the core and surrounding magneticelements, downward movement of the shell mounting fixture 48 iscontrolled so that the opposite ends 38a and 38b of the shell extendabove and below, respectively, the upper and lower end plates 14a and14b, as shown in FIG. 6(c). As will be described, the end extensions ofthe shell are formed or crimped radially inwardly over the marginalperipheral edges of the end plates so as to maintain the end platessnugly against the opposite ends of the core. In some applications, itmay be desirable to eliminate the extending ends of shell 16 bydecreasing the overall length of the shell. In such applications, theend plates 14a and 14b may be held in place by interference fits betweenthe outer peripheral edges of the end plates and the corresponding innersurfaces of shell 16, or by adhesives or other suitable means.

After the shell 16 is assembled over the core 12 and surroundingmagnetic elements, as shown in FIG. 6(c), the upper shell mountingfixture 48 is raised, shell guide sleeve 100 is removed, and boltassembly 58, with core 12, end plates 14a and 14b, magnetic elements 22and shell 16 in place, is removed from the lower support fixture 56. Aperiod of approximately 24 hours may be required for curing the adhesivebetween core 12, magnetic elements 15 and end plates 14a and 14bdepending upon the type of adhesive utilized, mixture ratios employed,environmental conditions, etc. However, subsequent assembly, shipping,and other operations may continue during the adhesive curing periodsince shell 16 acts as a clamp to firmly hold the assembled componentstogether until the adhesive cures.

FIGS. 8(a)-8(f) illustrate sequentially the final operation in theassembly method of the present invention. This final operation is acrimping operation in which the ends of the shell extending beyond theircorresponding end plates 14a,b are deformed generally radially inwardlyover the peripheral edges of the end plates 14a and 14b. This operationis preferably conducted in incremental steps in, for example, threesteps. In the illustrated embodiment, these steps involve the use ofcrimping dies 122, 124, and 126. Other methods or techniques, such rollforming, may also be employed to deform the axially extending ends ofshell 16 in the desired manner.

As illustrated in FIGS. 8(a) and 8(b), the crimping die 122 has an innerbore 126 defined by a cylindrical surface 128 and an inwardly taperedannular surface 130. The cylindrical surface 128 has a diametersubstantially equal to or slightly larger than the maximum outerdiameter of rotor 10. The annular surface 130 is tapered at an angle ofapproximately 30 relative to the center axis of cylindrical surface 128.With the crimping die 122 positioned in overlying axial alignment with arotor subassembly as illustrated in FIG. 8(b), application of apredetermined force F1 to crimping die 122 causes the extending end 38aof the shell to be crimped or deformed by the tapered surface 130inwardly over the peripheral edge of the end plate 14a toward thecentral axis of the rotor.

A second crimping die 124, having a bore 132 similar to bore 127 butdefining an annular surface 134 tapered at an angle of approximately 60relative to its center axis, is employed to further crimp the extendingend 38a of the shell. Thus, application of a further predetermined forceF2 to the crimping die 124 causes the end extension 38a of the shell tobe further crimped or deformed over the peripheral edge of the end plate14a, as illustrated in FIG. 8(d).

The final step in the crimping operation employs a crimping die 126which differs from the crimping dies 122 and 124 in that die 126 has acentral bore which terminates in a substantially flat end surface 136normal to the bore axis. Upon application of a predetermined force F3,the end surface 136 engages the partially crimped end 38a of the shelland flattens it against the outwardly facing peripheral edge surface ofthe end plate 14a, as illustrated in FIG. 8(f). The crimping die 126 ispreferably provided with an insert 138 which may be made of anelastically deformable but firm material such as Teflon, nylon or hardrubber that engages the outer annular surface of the shell 16 as thecrimping die 126 undergoes movement to complete the crimping operation.The inside diameter of insert 138 is made slightly smaller than themaximum outer diameter of rotor 10 so as to effect a press fit againstthe periphery of the shell. The insert 138 serves to minimize bulging ofthe outer diameter of shell 16 encircled by the insert during a crimpingoperation, thereby maintaining the shell end diameters within thedesired maximum outer diameter of the rotor. The insert 138 alsoprevents wedging of shell 16 within the crimping die during the crimpingoperation.

Preferably both of the end extensions 38a and 38b of shell 16 aresimultaneously crimped or formed radially inwardly over the outermarginal edges of the corresponding end plates 14a,b prior to removingthe rotor from the bolt assembly 58. The shell ends 38a and 38b arecrimped simultaneously to avoid axial displacement of the magneticelements 15 relative to the core 12 and shell 16 by application ofcrimping ram forces F1, F2, or F3. The crimping operation is preferablyperformed prior to adhesive cure and prior to removal of the rotor 10from bolt assembly 58 so that the bolt assembly provides support forboth end plates 14a and 14b during the crimping operation. Further thecrimping force applied to the shell end extension 38a is controlled soas to prevent bowing or bending of the outer periphery of the end plate14a which overlies the gap 40 and any uncured resin in the gap.

Referring to FIGS. 9(a), 9(b), 10, 11(a), and 11(b), the spacing andgauge device 110 and clamping devices 112 are supported on a base plate56a of the base support 56 so as to lie generally in a plane parallel toand spaced above the base plate 56a and intersecting the midpoint of thelongitudinal axis of a core 12 when supported by the bolt assembly 58 onthe base support 56. For purposes of clarity, the upper end plate 14a,alignment guide 84 and hold down nut 98 are not shown in the plan viewsof FIGS. 9(a), 10 and 11(a).

The spacing and gauge device 110 includes three radially movable gaugemembers, indicated generally at 140, which are spaced at 120° intervalsabout the axis of the base support 56. Each gauge member 140 includes awedge-shaped gauge tip 142 mounted on the inner end of a support arm144. Each support arm 144 is supported on the upper end of a stand 146for longitudinal movement radially of the longitudinal axis of basesupport 56. Each support arm 144 carries a cam follower in the form of aroller 148 rotatable on a roller support shaft 150 which depends fromthe corresponding support arm. The cam follower rollers 148 are receivedwithin respective cam slots 152 formed in a generally flat actuatingring 154 supported on the stands 146 concentric to and rotatable aboutthe center axis of base support 56. An operating handle 156 is fixed tothe actuating ring 154 and is engagable with an adjustable stop 158supported on the base plate 56a to limit rotation of the actuating ringin a clockwise direction, as viewed in FIG. 9(a).

As illustrated in FIG. 9(a), when three magnetic elements 15 aremanually placed against and adhesively adhered to the outer cylindricalsurface 26 of a core 12 supported on the base support 56, unequalarcuate gaps are generally created between adjacent longitudinal edgesof the magnetic elements, notwithstanding that each magnetic element isinitially positioned between two longitudinal ribs or beads 26a formedon the outer core surface. If assembly of the rotor were completed withunequal spacing between the magnetic elements, severe imbalance of therotor would result during high speed operation, with adverseconsequences.

The gauge tips 142 and associated support arms and cam slots 152 areconfigured to effect simultaneous equal radial movement of the gaugetips upon rotation of the actuating ring 154. In the illustratedembodiment, rotation of the actuating ring 154 in a clockwise direction,as viewed in FIGS. 9(a) and 10, until the handle 156 engages thepre-adjusted stop 158, causes each gauge tip 142 to move radiallyinwardly and wedge between the adjacent longitudinal edges of twoadjacent magnetic elements disposed against the core. Such movement ofthe gauge tips causes the magnetic elements to move circumferentiallyabout the core 12 until the magnetic elements are equally arcuatelyspaced or gauged from each other.

To release the gauge tips 144 from the magnetic elements 15, theactuating ring 154 is rotated in a counterclockwise direction. While theillustrated embodiment employs a manually operated actuating ring toactuate the gauge tips 142, it will be appreciated that the actuatingring may be adapted for automatic operation by pneumatics, hydraulics,an electric motor, or other suitable means. Alternatively, the gauge tipsupport arms 144 may be individually actuated by suitable automaticcontrol means operative to effect equal simultaneous movement of thegauge tips.

As illustrated in FIGS. 9(a), 10 and 11(a), the three clamping devices112 are equally angularly spaced between gauge members 140 about thecenter axis of the support base 56. Each clamping device 112 includes asupport bracket 162 mounted on the base plate 56a, as by screws 162a,and has a clamping member 164 having an arcuate clamping surface 164a onwhich is preferably secured a compressible elastic material, such as asponge rubber pad 166. Each clamping member 164 is adjustably mounted ona support rod 168 which is reciprocally slidable in a guide bracket 170affixed on the upper end of a corresponding support bracket 162. Thesupport rods 168 extend radially from the axis of the base support 56and lie generally in the plane of the gauge support arms 144. The outerend of each support rod 168 is operatively connected to an actuatinglever or handle 172 through a linkage arrangement 174. Each actuatinglever 172 is pivotally connected at 172a to its corresponding linkagearrangement 174, and is pivotally connected at 172b to the outer end ofthe corresponding guide bracket 170. The actuating levers 172 areconfigured such that pivotal movement of the actuating levers betweenoutwardly extending positions, as shown in solid lines in FIG. 9(b), andinwardly extending positions, as shown in phantom in FIG. 9(b), effectsreciprocating movement of the corresponding clamping members 164. Thelevers 172 are also configured to cause their associated pivotalconnections 172a to undergo an over-center action relative to thecorresponding pivot axes 172b so as to releasably lock the clampingmembers 164 in clamping positions when the levers 172 are in theirinward positions. Three upstanding support blocks 176 are affixed to thebase plate 56a so as to slidably support the clamping members 164 andalso provide support for the gauge member actuating ring 154.

Following circumferential positioning or spacing of the magneticelements 15 by the spacing means 110, the clamp actuating levers 172 areactuated to cause the clamping members 164 to engage the outer surfacesof their respective magnetic elements 15, and clamp the magneticelements against the core 12. During assembly of a shell 16 over a coreand surrounding magnetic elements, the gauge tips 142 and clampingmembers 164 are moved outwardly from the core and magnetic elements whenthe shell has advanced to approximately one-half the longitudinal lengthof the core, so as to allow continued cold-pressing of the shell 16downwardly over magnetic elements. Thus, the clamping members 164provide a means for temporarily securing the magnetic elements 15 inposition against the core 12 until shell 16 has advanced sufficiently toassume this function. Although the clamping members 164 are shown asbeing manually operated, power operated clamps, with or withoutautomatic controls, may also be used.

Summarizing the operation of the described rotor assembly apparatusduring assembly of a permanent magnet rotor 10, a suitable adhesive,such as Epon 828 epoxy, is applied to the outer cylindrical surface of arotor core 12 so as to provide a minimum coverage of approximately 80%of the outer cylindrical surface. A layer of similar adhesive is appliedto one surface of the lower end plate 14b which is placed on the annularsurface 76 on the bolt assembly 58 with the adhesive surface facingupwardly. The base 60 of the bolt assembly 58 may then be positioned inthe support fixture 56 which is mounted in a press or similar apparatushaving a ram 49. The core 12 is then placed on the bolt assembly withthe boss 80 received within the axial bore 18 and with the core orientedsuch that the alignment pin 72 is received within the locating bore 74in the lower end of the core, thus, positioning the core inpredetermined orientation to the support base 56 and associated spacingand gauge members 110 and clamping members 112.

After positioning the core 12 and lower end plate 14b onto the boltassembly 58, three magnetic elements 22 are placed around the corebetween the longitudinal ribs 26a. The spacing and gauging devices 110are then actuated to cause the wedging shaped tips 142 to effect equalarcuate spacing between the magnetic elements. The clamping devices 112are then actuated through their respective operating levers 172 to bringthe clamping members 164 into clamping relation with the correspondingmagnetic elements to temporarily hold them in position against the corewith the lower ends of the magnets engaging the adhesive covered surfaceof the lower end plate 14b. As aforedescribed, the core 12 has a greaterlongitudinal length than the longitudinal lengths of the magneticelements 22, thereby establishing a space or gap between the upper endsof the magnets and a plane containing the upper end surface of the core12. An adhesive, such as Epon 828 epoxy, is applied in a generallycircular bead to the upper ends of the magnetic elements, and the topend plate 14a is placed on the upper end of the rotor. The alignmentguide 84 is then placed over the upper end of shank 82 such that thelocating boss 90 seats within the circular center opening in the upperend plate 14a to axially align the upper end plate with core 12 and thelower end plate 14b. The retaining nut and washer 98 and 96 are thenmounted on shank 82 to firmly secure the alignment guide 84 in assembledrelation. The adhesive applied to the upper ends of the magnets isapplied in such quantity as to fill the annular gap or space between theupper end plate and the upper ends of the magnets to a minimum of 40%and a maximum of 80%, thus assuring at least 20% void between the upperend plate and the magnets upon curing of the adhesive. By intentionallylimiting the amount of adhesive applied between the upper ends of themagnetic elements 15 and the upper end plate 14a, no adhesive will besqueezed outwardly when the upper end plate is secured against the coreend by the alignment guide 84 even though the longitudinal lengths ofthe magnets may vary significantly due to tolerance variations. Thisprevents adherence of the adhesive to the assembly apparatus withattendant problems.

The shell guide sleeve 100 is then placed over the upper alignment guide84 so as to rest on the upper surface of the upper end cap 14a. Astainless-steel shell 16 is then placed over the outer surface of theshell guide sleeve. After placing a shell 16 over the guide sleeve 100,the upper shell mounting fixture 48 is brought downwardly by actuationof the associated press ram 49 to effect cold-pressing of the shell 16downwardly over the rotor and surrounding magnets as aforedescribed, thegauging and clamping devices 110 and 112 being retracted during downwardmovement of the shell.

Following assembly of the shell 16 over the core and surroundingmagnetic elements such that ends of the shell extend axially below andaxially above the lower and upper end plates 14b and 14a, respectively,the bolt assembly 58 is removed from the base support 56 and the endextensions of the shell are crimped or formed generally radiallyinwardly over the adjacent peripheral marginal edges of the end platesso as to retain the end plates snugly against the opposite ends of thecore without causing the end plates to bow or become dish-shaped, asaforedescribed.

It has been found that the force required to cold-press the shell 16axially onto a core and surrounding magnetic elements having an outerdiameter of approximately 3" may vary widely, depending upon therelative dimensional variations of the various components and thephysical characteristics, such as hardness and yield strength, of themetallic material from which the shell 16 is made. However,notwithstanding variations in dimensional and physical properties of thecore 12, magnetic elements 15 and shell 16, the rotor assembly apparatusin accordance with the present invention provides precise fixturing ofthe various components in desired aligned relation so as to accommodatevarying dimensional and physical characteristics without impeding theassembly process. Shells of nominal three-inch diameter made fromannealed 304 stainless-steel welded seam tubing, which afterseam-welding, is cold-worked to decrease the wall thickness to 0.008"and to increase the yield strength of all portions of the tubing toapproximately 80,000 psi to 120,000 psi have been found to providesatisfactory results in the rotor 10. Satisfactory results are alsobelieved possible using materials having other characteristics, orcombinations of characteristics, suitable for particular applications.

It is noted that while the assembly apparatus and method described aboveemploys a movable fixture to press a tubular shell over the core andsurrounding magnetic elements, which act as a mandrel to reform theshell, it is contemplated that the shell may be held stationary whilethe core and magnetic elements are pressed axially into the shell.

While preferred embodiments of the rotor assembly and the apparatus andmethod for making the same have been illustrated and described, it willbe understood that changes and modifications may be made therein withoutdeparting from the invention in its broader aspects. Various features ofthe invention are defined in the following claims.

What is claimed is:
 1. Apparatus for making a permanent magnetizablerotor having a generally cylindrical core and a plurality of generallysimilar size magnetizable elements spaced about the circumference of thecylindrical core, each of said magnetizable elements having longitudinaledges and an inner arcuate surface dimensioned so that the sum of theinner arcuate surface dimensions of said plurality of magnetizableelements is less than the circumference of said cylindrical core, saidapparatus comprising, in combination, a support fixture for supportingthe core in a fixed position, a plurality of gauges each having agenerally convex tip and being supported for movement radially of thelongitudinal axis of a core when supported on said support fixture, anactuator operatively associated with said gauges and operative to effectsubstantially equal simultaneous radial movement of said gauge tips sothat each tip is wedged between adjacent longitudinal edges of twoadjacent magnetizable elements disposed against said core to cause saidmagnetizable elements to move circumferentially about said core untilequally spaced from each other, and a plurality of clamps supportedintermediate said gauges for movement generally radially of thelongitudinal axis of a core when supported on said fixture, said clampseach being movable to engage an outer exposed surface of a magnetizableelement so as to clamp said magnetizable elements against said coreindependently of said gauges after equally spacing said elements fromeach other.
 2. Apparatus according to claim 1 including an adjustablestop adapted for cooperation with said actuator so as to limit theextent of radial movement of said gauge tips toward the core whenmounted on the support fixture.
 3. Apparatus as defined in claim 1wherein said convex tips are substantially V-shaped.
 4. Apparatusaccording to claim 1 wherein each gauge has a roller having a surfacefor contacting a camming surface, and wherein said actuator meanscomprises a movable member having at least one camming surface disposedadjacent each roller such that movement of the movable member causescorresponding radical movements of the gauges in accordance withcontours of the respective camming surfaces.
 5. Apparatus according toclaim 4 wherein said movable member has a plurality of generallycircumferential slots defining said camming surfaces, and wherein eachgauge roller is disposed in a corresponding one of said slots forinteraction with the corresponding camming surfaces when said movablemember is moved.
 6. Apparatus according to claim 1 wherein each clampincludes an end portion for contacting a corresponding one of saidmagnetizable elements, actuator means for moving said end portions intoclamping relation with the corresponding magnetizable elements, andmeans for releasably locking said end portions in said clampingrelation.
 7. Apparatus according to claim 6 wherein each of said endportions includes an elastic element for engaging the correspondingmagnetizable element when the end portion is moved into said clampingrelation.